Modulatory Effects of the Er,Cr:YSGG—Diode Laser Combination Irradiation on Human Osteoblasts—Might Be Relevant for Periapical Bone Regeneration?

Abstract

This in vitro study evaluated how Er,Cr:YSGG irradiation at three energy levels (1, 3, and 6 J/cm2), 810 nm diode irradiation, and their combinations can influence human osteoblast viability and osteogenic activity. Human osteoblasts (hOB) were assigned to eight groups: control, diode, Er,Cr:YSGG at 1, 3, and 6 J/cm2, and each Er,Cr:YSGG dose followed immediately by diode irradiation. 24 h after irradiation, metabolic activity (MTT), membrane integrity (LDH), nitric oxide (NO) production, and alkaline phosphatase (ALP) activity were assessed, and cell morphology was tracked by holographic live-cell imaging. Cell viability and membrane integrity were preserved across all protocols (MTT p = 0.325; LDH p = 0.057; both n.s.), and live-cell imaging showed osteoblast morphology and proliferation. Diode irradiation significantly increased ALP activity versus control (12.96 vs. 5.40 IU/L; p = 0.011), confirming a biostimulatory osteogenic effect, whereas Er,Cr:YSGG at 6 J/cm2 almost completely suppressed ALP activity (0.42 IU/L; p < 0.001 vs. diode). Both Er,Cr:YSGG 3 J + diode and 6 J + diode combinations significantly attenuated the diode-induced ALP increase and NO elevation in a dose-dependent manner. No protocol was cytotoxic. The 810 nm diode laser was the most osteogenically favorable condition, whereas higher-energy Er,Cr:YSGG irradiation suppressed ALP activity and, when combined with the diode, attenuated its osteogenic effect.